JP2019203863A - Wavefront sensor, wavefront measuring device, optical element manufacturing method, and optical system manufacturing method - Google Patents

Abstract

To realize a low-cost wavefront sensor that dispenses with the mechanism and process for fine-adjusting the relative positions of a beam dividing element and an imaging element.SOLUTION: The wavefront sensor comprises a beam dividing element for dividing the light to be detected into a plurality of lights, an imaging element for receiving the plurality of lights, and computation means for calculating the wavefront of the light to be detected, on the basis of the intensity distribution of the plurality of lights having been received by the imaging element. The beam dividing element and the imaging element are in contact, or a reference plate glass is included between the beam dividing element and the imaging element, the reference plate glass being in contact with both of the beam dividing element and the imaging element. When calculating the wavefront of the light to be detected, the computation means corrects the positional deviation of the relative positions of the beam dividing element and the imaging element from a design position by a computation that involves rotating the positional deviation around a specific axis.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wavefront sensor that measures a wavefront of an optical element or an optical system.

  Wavefront sensors such as Shack-Hartmann sensors and Talbot interferometers are used for wavefront measurement of transmitted light or reflected light of optical elements and optical systems. The wavefront sensor includes a light beam splitting element (two-dimensional microlens array or two-dimensional diffraction grating) that splits a light beam into a plurality of lights, and an image sensor (CMOS or CCD) that receives the plurality of lights. The measurement accuracy of the wavefront sensor depends on the relative position accuracy of the light beam splitting element and the image sensor.

  The wavefront sensor disclosed in Patent Document 1 is provided with a mechanism for accurately adjusting the relative position of the light beam splitting element and the imaging element.

Special table 2012-533758 gazette

  The wavefront sensor disclosed in Patent Document 1 is premised on the precise adjustment of the relative position of the light beam splitting element and the imaging element. Therefore, the cost of the wavefront sensor is increased by the precision adjustment mechanism and the precision adjustment process.

  An object of the present invention is to provide a low-cost wavefront sensor that omits a mechanism and a process for precisely adjusting the relative position of a light beam splitting element and an imaging element.

  A wavefront sensor according to an embodiment of the present invention includes a light beam splitting element that divides test light into a plurality of lights, an imaging element that receives the plurality of lights, and an intensity of the plurality of lights received by the imaging element. Computing means for calculating the wavefront of the test light based on the distribution, wherein the light beam splitting element and the image sensor are in contact, or a reference flat glass between the light beam splitting element and the image sensor And the reference flat glass is in contact with both the light beam splitting element and the image sensor, and the calculating means calculates a relative wavefront of the light beam splitting element and the image sensor in calculating the wavefront of the test light. The positional deviation is corrected by an operation of rotating around a specific axis.

  A wavefront measuring apparatus according to another embodiment of the present invention includes a light source, a light projecting system for causing light from the light source to enter a test optical system, and the wavefront sensor described above.

  An optical system manufacturing method according to another embodiment of the present invention includes: assembling an optical system; and measuring the wavefront aberration of the optical system using the wavefront measuring device described above, thereby improving the optical performance of the optical system. The method includes a step of evaluating.

  An optical element manufacturing method according to another embodiment of the present invention includes: a step of processing an optical element; and measuring the wavefront aberration of the optical element using the wavefront measuring device described above. The method includes a step of evaluating.

  According to the present invention, it is possible to obtain a low-cost wavefront sensor that omits a mechanism and a process for precisely adjusting the relative position of a light beam splitting element and an imaging element.

1 is a diagram illustrating a schematic configuration of a wavefront sensor according to Embodiment 1. FIG. FIG. 5 is a diagram illustrating a schematic configuration of a wavefront sensor according to a second embodiment. The figure which shows schematic structure of the wavefront sensor in case the cover glass of an image pick-up element is distorted. FIG. 6 is a diagram illustrating a schematic configuration of a wavefront measuring apparatus according to a third embodiment. The figure which shows the manufacturing process of the manufacturing method of an optical system. The figure which shows the manufacturing process of the manufacturing method of an optical element.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration of a wavefront sensor 100 according to the first embodiment of the present invention. The wavefront sensor 100 includes a light beam splitting element (microlens array) 10, a reference flat glass 20, an imaging element (for example, CMOS or CCD) 30, and an arithmetic means (computer) 80. With respect to the surface 30a of the image pickup device 30 (light receiving unit in this embodiment), an x axis and ay axis are defined in the horizontal direction, and a z axis is defined in the vertical direction. The x-axis and y-axis directions coincide with the two-dimensional arrangement direction of the pixels of the image sensor 30. The surface 30a of the image sensor 30 is at the position of z = 0.

  The light incident side surface (first surface) 10a of the light beam splitting element 10 has a lens structure (function to split the light beam), and the light output side surface (second surface) 10b is a flat surface. The light incident side surface (first surface) 20a and the light emission side surface (second surface) 20b of the reference flat glass 20 are both flat surfaces, and the first surface 20a and the second surface 20b are parallel to each other. (The angle formed by the first surface 20a and the second surface 20b is 0.005 degrees or less). The second surface 10b of the light beam splitting element 10 and the first surface 20a of the reference flat glass 20 are in contact with each other, and the second surface 20b of the reference flat glass 20 and the surface 30a of the imaging device 30 are in contact with each other.

When parallel light is incident on the wavefront sensor 100, the thickness _Tm and the refractive index N of the light beam splitting element 10 are formed so that the condensing point of each lens of the light beam splitting element 10 is substantially formed on the surface 30a of the image sensor 30. _m , the thickness T _p of the reference flat glass 20, and the refractive index N _p are selected. For example, selection is made so as to satisfy Formula 1.

・・・数式１

... Formula 1

  Here, f is a focal length of each lens of the light beam splitting element 10.

  The wavefront sensor 100 does not include a mechanism for precisely adjusting the relative position between the light beam splitting element 10 and the imaging element 30. Further, when assembling the wavefront sensor 100, the precision adjustment step is omitted, and the light beam splitting element 10, the reference flat glass 20, and the imaging element 30 are fixed with a jig (not shown) so as to be in contact, or with an adhesive or the like. Just fix it. When an adhesive is used, the adhesive is not applied to the surfaces (10b and 20a, 20b and 30a) in contact with each element, but is applied to the side surfaces (surfaces through which light is not transmitted). Instead of using an adhesive, it may be bonded by optical contact.

  In the present embodiment, the light beam splitting element 10 and the image sensor 30 are in contact with the reference flat glass 20, so that the relative positions of the light beam splitting element 10 and the image sensor 30 in the z direction are positioned with high accuracy. That is, the distance between the first surface 10a of the light beam splitting element 10 and the surface 30a of the imaging element 30 is constant. Therefore, precise adjustment of the relative position in the z direction, which has been conventionally performed, can be omitted. On the other hand, the arrangement direction of the microlenses of the light beam splitting element 10 and the arrangement direction of the pixels of the imaging element 30 (= x direction, y direction) do not match due to the effect of omitting the fine adjustment. That is, the arrangement direction of the microlenses of the light beam splitting element 10 is rotated around the z axis (the axis orthogonal to the surface 30a of the imaging element 30) with respect to the arrangement direction of the pixels of the imaging element 30. The relative position error due to the rotation around the z axis (specific axis) is corrected by a calculation process described later.

When the test light 90 having a certain wavefront W (x, y) is incident on the wavefront sensor 100, a condensing spot corresponding to the wavefront shape is formed on the surface 30a of the image sensor 30 as shown in FIG. . Then, the image sensor 30 receives the intensity distribution of the condensed spot (intensity distribution of a plurality of lights). The intensity distribution data received by the image sensor 30 is sent to the computer 80, and the barycentric coordinates of each focused spot are calculated. The coordinates of the microlens located in the i row and j column of the light beam splitting element 10 are (X _ij , Y _ij , T _m + T _p ), and the barycentric coordinates of the condensing spot formed by the lens are (X _ij + δX _ij , Y _ij + δX _ij , 0), the relational expression of Expression 2 is established. Here, φ _xij and φ _yij are incident angles in the x direction and the y direction incident on each microlens.

・・・数式２

... Formula 2

  If the angle of the light incident on each microlens is small, Equation 2 can be approximated using Equation 1 as Equation 3.

・・・数式３

... Formula 3

It is assumed that the arrangement direction of the microlenses of the light beam splitting element 10 and the arrangement direction of the pixels of the image sensor 30 are substantially the same (that is, when fine adjustment is performed as usual). At this time, the coordinates X _ij and Y _ij of the microlens of the light beam splitting element 10 are arranged in the x direction and the y direction with the period of the microlens of the light beam splitting element 30 (for example, Λ = 150 μm) as in Expression 4. Value.
X _ij = Λj + a
Y _ij = Λi + b
... Formula 4

  Here, a is an x-coordinate offset constant and b is an y-coordinate offset constant. On the other hand, in this embodiment, since the arrangement direction of the microlenses of the light beam splitting element 10 is rotated around the z axis (specific axis) with respect to the arrangement direction of the pixels of the image pickup element 30, It is necessary to correct.

・・・数式５

... Formula 5

Here, θ _z is a relative position error due to rotation around the z axis. The amount of theta _z is in advance calculated from the centroid coordinate array of the focused spot as measured by image sensor 30 when is incident parallel light to the wavefront sensor 100. By combining Formula 5 with Formula 2 or Formula 3, the wavefront W (x, y) of the test light can be calculated. Even without precise adjustment there are times when a small value of accidental θ _z. In that case, Formula 4 may be used instead of Formula 5.

  As described above, in this embodiment, the light beam splitting element 10 and the image sensor 30 are arranged so as to be in contact with the reference flat glass 20, so that the relative position in the z direction of the light beam split element 10 and the image sensor 30 can be accurately determined. Positioning. The relative position error due to rotation around the z-axis (specific axis) is corrected by the calculation of Equation 5, thereby eliminating the precision adjustment mechanism and the precision adjustment process and realizing a low-cost wavefront sensor. . The present embodiment also has the following effects.

  In the conventional fixing method for holding the outside of the effective region (≈peripheral portion) of the light beam splitting element 10, the light beam splitting element 10 is affected by the deformation of the light beam splitting element 10 due to its own weight deformation, stress deformation, thermal expansion / heat shrinkage. A non-linear distribution may occur in the distance between the image sensor 10 and the image sensor 30 in the z direction. Here, the non-linear distribution is, for example, a distribution such as a quadratic function (+ high order function) having a concave or convex shape at the center of the effective region. On the other hand, in the present embodiment, since the reference flat glass 20 supports the entire effective area of the light beam splitting element 10, it is possible to suppress the nonlinear distribution as described above. That is, a robust wavefront sensor can be realized.

In this embodiment, the refractive index N _p of the refractive index N _m and reference plate glass 20 of the light-flux splitter 10 is different (i.e., the material of the beam splitting element 10 and the reference plate glass 20 are different) has been described on the assumption that both May have the same refractive index (material). In this case, in Equation 2, Equation 3, the _T m + _{T p} to _{T m,} by an expression obtained by substituting 0 into _{T m.} If the light beam splitting element 10 having the thickness T _m + T _p can be manufactured, the reference flat glass 20 may be omitted. In this case, the light beam splitting element 10 and the image sensor 30 are in direct contact. Generally, a microlens array manufactured by photolithography has a thickness of about 1 mm. To remove the reference plate glass 20 by increasing the thickness of the light-flux splitter 10, for example, focal length f~5mm of microlenses, when the refractive index _N m to 1.5 of the microlens array, the thickness ~7.5mm It is necessary to prepare a microlens array of about 7 to 8 times the conventional size.

In the present embodiment, the first surface 10a of the light beam splitting element 10 is a lens structure and the second surface 10b is a flat surface, but the first surface 10a is a flat surface and the second surface 10b is a lens structure (or the first surface 10a). The second surface 10b may have a lens structure). In that case, it is necessary to prepare the reference flat glass 20 satisfying f = T _p / N _p instead of Equation 1. Equations 2 and 3 are obtained by substituting 0 for _Tm .

In this embodiment, as shown in Equation 5, the calculation of rotating the coordinates of the microlens of the light beam splitting element 10 by θ _z is performed, but instead, the shift amounts δX _ij and δX of the center-of-gravity coordinates of each focused spot _ij may be rotated - [theta] _z of.

  In this embodiment, a Shack-Hartmann sensor using a microlens array as the light beam splitting element 10 is used as the wavefront sensor. Instead, a Hartmann sensor using a pinhole array or a Talbot interferometer using a diffraction grating is used. May be. The wavefront recovery method may be a method of calculating the barycentric coordinates of each focused spot as in this embodiment, or a Fourier transform method.

  FIG. 2 shows a schematic configuration of the wavefront sensor 200 according to the second embodiment of the present invention. The same configurations as those in the first embodiment will be described with the same reference numerals. The wavefront sensor 200 includes a light beam splitting element 10, a reference flat glass 20, an imaging element 30 having a cover glass 35, and a computer 80. In this embodiment, the cover glass 35 and the image pickup device 30 are defined, and the surface 30 a of the image pickup device 30 means the surface of the cover glass (light transmission member) 35. It is assumed that there is an air layer between the cover glass 35 and the light receiving unit 30b of the image sensor 30.

In this example, since there is a layer of cover glass 35 (thickness T _c , refractive index N _c ) and air (thickness T _a , refractive index 1) in addition to the configuration of FIG. Equations 1 and 2 correspond to Equations 6 and 7, respectively. In the configuration of the present embodiment, the wavefront of the test light can be calculated by combining Expression 5 and Expression 7 (or an expression obtained by substituting f of Expression 6 into Expression 3).

・・・数式６

... Formula 6

・・・数式７

... Formula 7

In the present embodiment, the cover glass 35 is provided in front of the light receiving unit 30b of the image sensor 30 (+ z-axis direction). However, a low-pass filter, an infrared cut filter, or a combination of these may be used instead of the cover glass. May be. Thickness T _k , refractive index N _k (k = 1, 2,...) From the light beam splitting surface 10a (surface having a lens or diffraction grating structure) of the light beam splitting device 10 to the light receiving unit 30b of the imaging device 30. .., M) When there is a layer, Equation 6 and Equation 7 are generalized as Equation 8 and Equation 9.

・・・数式８

... Formula 8

・・・数式９

... Formula 9

  In the above description, it is assumed that the cover glass 35 is attached to the light receiving unit 30b in parallel and without distortion in the imaging element 30. However, depending on the imaging device to be used, the cover glass 35 may be attached with poor accuracy as in the wavefront sensor 201 of FIG. In this case, the light beam splitting element 10 and the reference flat glass 20 are inclined with respect to the light receiving portion 30b of the image sensor 30 (relative position errors are caused by rotation around the x axis and the y axis). If the area of the light beam splitting element 10 is, for example, 15 × 15 mm and the thickness of the reference flat glass 20 is, for example, about 5 mm, the portion constituted by the set of the light beam splitting element 10 and the reference flat glass 20 has almost no distortion. Can be arranged. When the light beam splitting element 10 has a large area, distortion can be suppressed by increasing the thickness of the reference flat glass 20 in accordance with the area.

In the case of the configuration of FIG. 3, the thickness T _m of the light beam splitting element 10, the thickness T _p of the reference flat glass 20, and the thickness T _c of the cover glass 35 can be regarded as constant regardless of the location (cover glass). 35, the thickness is almost constant just by changing the shape. On the other hand, the thickness of the air layer (the thickness obtained by adding not only the air layer between the cover glass 35 and the light receiving surface 30b but also the air layer between the second surface 20b of the reference flat glass 20 and the surface 30a of the image sensor 30). _{Has a} distribution (T _a = T _a (X _ij , Y _ij ) = T _aij ). If this thickness distribution T _aij is ignored, a wavefront calculation error occurs. Conventionally, the light beam splitting element 10 is precisely adjusted to remove this distribution. However, in this embodiment, instead of the precise adjustment, correction calculation of the thickness of the air layer (x axis and y axis are used as specific axes). The conventional precision adjustment mechanism and process are omitted by performing a correction calculation by rotation around the axis.

In the configuration of the present embodiment, it can be considered that the set of the light beam splitter 10 and the reference flat glass 20 is tilted without distortion. Therefore, the thickness distribution T _aij of the air layer is a distribution that varies linearly as in Expression 10. Can be approximated.
T _aij = T _a + AX _ij + BY _ij
... Formula 10

Here, A, and B proportional constant, T _a is the average value of the thickness distribution of the air layer. The second term and the third term of Expression 10 are arctan (√ (A ² + B) with respect to an axis (axis parallel to the surface 30a of the image sensor 30) rotated arctan (B / A) from the y axis in the xy plane. ² )) Means that rotating correction is added. If the wavefront is calculated by substituting T _aij in Equation 10 into T _a in Equation 7, the wavefront in the wavefront sensor having the configuration of FIG. 3 can be obtained.

  FIG. 4 shows a schematic configuration of the wavefront measuring apparatus 1 using the wavefront sensor 100 of the first embodiment. The wavefront measuring apparatus 1 includes a light source 50, a light projecting system 60, and a wavefront sensor 100, and measures the wavefront of the test object 70. In this embodiment, the test object 70 is an optical system in which a plurality of optical elements are combined or a single optical element.

  The diverging light emitted from the light source 50 is converged by the light projecting system 60 and enters the test object 70. The light transmitted through the test object 70 enters the wavefront sensor 100, and the wavefront aberration 90 of the test object 70 is measured. The measurement result of the wavefront aberration can be fed back to the optical system and the optical element manufacturing method. As the light source 50, for example, a laser diode or an LED is used. The light projecting system 60 includes, for example, a single lens, a plurality of lenses, and a CGH (Computer-Generated Holography). According to the present embodiment, a low-cost wavefront measuring device can be realized by using a wavefront sensor that omits a mechanism and a process for precisely adjusting the relative position of the light beam splitting element and the imaging element.

  FIG. 5 shows a method for manufacturing the optical system. First, an optical system is assembled using a plurality of optical elements, and the position of each optical element is adjusted (S11). The optical performance of the assembled and adjusted optical system is evaluated (S12), and if the accuracy is insufficient, the assembly and adjustment are performed again. For this optical performance evaluation, the wavefront measuring apparatus 1 including the wavefront sensor of the first embodiment or the second embodiment can be used.

  FIG. 6 shows a method of manufacturing an optical element using mold processing. The optical element is manufactured through an optical element design process (S21), a mold design process (S22), and an optical element mold process (S23) using the designed mold. The molded optical element is evaluated for its shape accuracy (S24). If the accuracy is insufficient, the mold is corrected (S25), and the molding is performed again. If the shape accuracy is good, the optical performance of the optical element is evaluated (S26). If the optical performance is low, the optical element whose optical surface is corrected is redesigned (S27). If the optical performance is good, the process proceeds to the mass production process (S28) of the optical element to be molded. The wavefront measuring apparatus 1 can be used for this optical performance evaluation. The manufacturing method of the optical element is not limited to a mold, and can be similarly applied to manufacturing an optical element by grinding and polishing.

  The embodiments described above are merely representative examples, and various modifications and changes can be made to the embodiments when the present invention is implemented.

DESCRIPTION OF SYMBOLS 10 Light beam splitting element 20 Reference | standard flat glass 30 Image pick-up element 80 Calculation means

Claims (11)

A light beam splitting element that splits the test light into a plurality of lights;
An image sensor for receiving the plurality of lights;
Calculating means for calculating a wavefront of the test light based on an intensity distribution of the plurality of lights received by the imaging device;
The light beam splitting element and the image sensor are in contact with each other, or a reference flat glass is provided between the light beam splitting element and the image sensor, and the reference flat glass is in contact with the light beam splitting element and the image sensor. And
In the calculation of the wavefront of the test light, the calculation means corrects a positional shift between the relative positions of the light beam splitting element and the imaging element by a calculation that rotates around a specific axis. .   The wavefront sensor according to claim 1, wherein the specific axis is an axis orthogonal to a surface of the image sensor.   The wavefront sensor according to claim 1, wherein the specific axis is an axis parallel to a surface of the image sensor.   The wavefront sensor according to any one of claims 1 to 3, wherein the calculation means calculates a wavefront of the test light based on a thickness and a refractive index of the reference flat glass. The light beam splitting element has a function of splitting a light beam on a light incident side surface, and a light output side surface is a plane,
The image sensor or the reference flat glass is in contact with a light emission side plane of the light beam splitting element,
5. The wavefront sensor according to claim 1, wherein the calculation unit calculates a wavefront of the test light based on a thickness and a refractive index of the light beam splitting element. The image sensor has a light transmitting member on the light incident side of the light receiving unit,
The light beam splitting element or the reference flat glass is in contact with the light transmission member of the imaging element,
The wavefront sensor according to any one of claims 1 to 5, wherein the calculation means calculates a wavefront based on a thickness and a refractive index of the light transmitting member.   The wavefront sensor according to claim 6, wherein the light transmission member includes at least one of a cover glass, a low-pass filter, and an infrared cut filter.   A reference flat glass is provided between the light beam splitting element and the imaging element, and an angle formed by a light incident side surface and a light emission side surface of the reference flat glass is 0.005 degrees or less. The wavefront sensor according to claim 1. A light source;
A light projecting system for causing light from the light source to enter the test object;
9. A wavefront measuring apparatus comprising the wavefront sensor according to claim 1, wherein the wavefront sensor according to any one of claims 1 to 8 calculates a wavefront of the test light by receiving the test light emitted from the test object. Assembling the optical system;
A method for manufacturing an optical system, comprising the step of evaluating the optical performance of the optical system by measuring the wavefront aberration of the optical system using the wavefront measuring apparatus according to claim 9. Processing the optical element;
A method for manufacturing an optical element, comprising the step of evaluating the optical performance of the optical element by measuring the wavefront aberration of the optical element using the wavefront measuring apparatus according to claim 9.

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